Function Get-PendingReboot {
    <#
.SYNOPSIS
    Gets the pending reboot status on a local or remote computer.

.DESCRIPTION
    This function will query the registry on a local or remote computer and determine if the
    system is pending a reboot, from either Microsoft Patching or a Software Installation.
    For Windows 2008+ the function will query the CBS registry key as another factor in determining
    pending reboot state.  "PendingFileRenameOperations" and "Auto Update\RebootRequired" are observed
    as being consistant across Windows Server 2003 & 2008.

    CBServicing = Component Based Servicing (Windows 2008)
    WindowsUpdate = Windows Update / Auto Update (Windows 2003 / 2008)
    CCMClientSDK = SCCM 2012 Clients only (DetermineIfRebootPending method) otherwise $null value
    PendFileRename = PendingFileRenameOperations (Windows 2003 / 2008)

.PARAMETER ComputerName
    A single Computer or an array of computer names.  The default is localhost ($env:COMPUTERNAME).

.PARAMETER ErrorLog
    A single path to send error data to a log file.

.EXAMPLE
    PS C:\> Get-PendingReboot -ComputerName (Get-Content C:\ServerList.txt) | Format-Table -AutoSize

    Computer CBServicing WindowsUpdate CCMClientSDK PendFileRename PendFileRenVal RebootPending
    -------- ----------- ------------- ------------ -------------- -------------- -------------
    DC01     False   False           False      False
    DC02     False   False           False      False
    FS01     False   False           False      False

    This example will capture the contents of C:\ServerList.txt and query the pending reboot
    information from the systems contained in the file and display the output in a table. The
    null values are by design, since these systems do not have the SCCM 2012 client installed,
    nor was the PendingFileRenameOperations value populated.

.EXAMPLE
    PS C:\> Get-PendingReboot

    Computer     : WKS01
    CBServicing  : False
    WindowsUpdate      : True
    CCMClient    : False
    PendComputerRename : False
    PendFileRename     : False
    PendFileRenVal     :
    RebootPending      : True

    This example will query the local machine for pending reboot information.

.EXAMPLE
    PS C:\> $Servers = Get-Content C:\Servers.txt
    PS C:\> Get-PendingReboot -Computer $Servers | Export-Csv C:\PendingRebootReport.csv -NoTypeInformation

    This example will create a report that contains pending reboot information.

.LINK
    Component-Based Servicing:
    http://technet.microsoft.com/en-us/library/cc756291(v=WS.10).aspx

    PendingFileRename/Auto Update:
    http://support.microsoft.com/kb/2723674
    http://technet.microsoft.com/en-us/library/cc960241.aspx
    http://blogs.msdn.com/b/hansr/archive/2006/02/17/patchreboot.aspx

    SCCM 2012/CCM_ClientSDK:
    http://msdn.microsoft.com/en-us/library/jj902723.aspx

.NOTES
    Author:  Brian Wilhite
    Email:   bcwilhite (at) live.com
    Date:    29AUG2012
    PSVer:   2.0/3.0/4.0/5.0
    Updated: 01DEC2014
    UpdNote: Added CCMClient property - Used with SCCM 2012 Clients only
       Added ValueFromPipelineByPropertyName=$true to the ComputerName Parameter
       Removed $Data variable from the PSObject - it is not needed
       Bug with the way CCMClientSDK returned null value if it was false
       Removed unneeded variables
       Added PendFileRenVal - Contents of the PendingFileRenameOperations Reg Entry
       Removed .Net Registry connection, replaced with WMI StdRegProv
       Added ComputerPendingRename
#>

    [CmdletBinding()]
    param (
        [Parameter(Position = 0, ValueFromPipeline = $true, ValueFromPipelineByPropertyName = $true)]
        [Alias("CN", "Computer")]
        [String[]]$ComputerName = "$env:COMPUTERNAME",

        [String]$ErrorLog
    )

    Begin { } ## End Begin Script Block
    Process {
        Foreach ($Computer in $ComputerName) {
            Try {
                ## Setting pending values to false to cut down on the number of else statements
                $CompPendRen, $PendFileRename, $Pending, $SCCM = $false, $false, $false, $false

                ## Setting CBSRebootPend to null since not all versions of Windows has this value
                $CBSRebootPend = $null

                ## Querying WMI for build version
                $WMI_OS = Get-WmiObject -Class Win32_OperatingSystem -Property BuildNumber, CSName -ComputerName $Computer -ErrorAction Stop

                ## Making registry connection to the local/remote computer
                $HKLM = [UInt32] "0x80000002"
                $WMI_Reg = [WMIClass] "\\$Computer\root\default:StdRegProv"

                ## If Vista/2008 & Above query the CBS Reg Key
                If ([Int32]$WMI_OS.BuildNumber -ge 6001) {
                    $RegSubKeysCBS = $WMI_Reg.EnumKey($HKLM, "SOFTWARE\Microsoft\Windows\CurrentVersion\Component Based Servicing\")
                    $CBSRebootPend = $RegSubKeysCBS.sNames -contains "RebootPending"
                }

                ## Query WUAU from the registry
                $RegWUAURebootReq = $WMI_Reg.EnumKey($HKLM, "SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate\Auto Update\")
                $WUAURebootReq = $RegWUAURebootReq.sNames -contains "RebootRequired"

                ## Query PendingFileRenameOperations from the registry
                $RegSubKeySM = $WMI_Reg.GetMultiStringValue($HKLM, "SYSTEM\CurrentControlSet\Control\Session Manager\", "PendingFileRenameOperations")
                $RegValuePFRO = $RegSubKeySM.sValue

                ## Query ComputerName and ActiveComputerName from the registry
                $ActCompNm = $WMI_Reg.GetStringValue($HKLM, "SYSTEM\CurrentControlSet\Control\ComputerName\ActiveComputerName\", "ComputerName")
                $CompNm = $WMI_Reg.GetStringValue($HKLM, "SYSTEM\CurrentControlSet\Control\ComputerName\ComputerName\", "ComputerName")
                If ($ActCompNm -ne $CompNm) {
                    $CompPendRen = $true
                }

                ## If PendingFileRenameOperations has a value set $RegValuePFRO variable to $true
                If ($RegValuePFRO) {
                    $PendFileRename = $true
                }

                ## Determine SCCM 2012 Client Reboot Pending Status
                ## To avoid nested 'if' statements and unneeded WMI calls to determine if the CCM_ClientUtilities class exist, setting EA = 0
                $CCMClientSDK = $null
                $CCMSplat = @{
                    NameSpace    = 'ROOT\ccm\ClientSDK'
                    Class        = 'CCM_ClientUtilities'
                    Name         = 'DetermineIfRebootPending'
                    ComputerName = $Computer
                    ErrorAction  = 'Stop'
                }
                ## Try CCMClientSDK
                Try {
                    $CCMClientSDK = Invoke-WmiMethod @CCMSplat
                }
                Catch [System.UnauthorizedAccessException] {
                    $CcmStatus = Get-Service -Name CcmExec -ComputerName $Computer -ErrorAction SilentlyContinue
                    If ($CcmStatus.Status -ne 'Running') {
                        Write-Warning "$Computer`: Error - CcmExec service is not running."
                        $CCMClientSDK = $null
                    }
                }
                Catch {
                    $CCMClientSDK = $null
                }

                If ($CCMClientSDK) {
                    If ($CCMClientSDK.ReturnValue -ne 0) {
                        Write-Warning "Error: DetermineIfRebootPending returned error code $($CCMClientSDK.ReturnValue)"
                    }
                    If ($CCMClientSDK.IsHardRebootPending -or $CCMClientSDK.RebootPending) {
                        $SCCM = $true
                    }
                }

                Else {
                    $SCCM = $null
                }

                ## Creating Custom PSObject and Select-Object Splat
                $SelectSplat = @{
                    Property = (
                        'Computer',
                        'CBServicing',
                        'WindowsUpdate',
                        'CCMClientSDK',
                        'PendComputerRename',
                        'PendFileRename',
                        'PendFileRenVal',
                        'RebootPending'
                    )
                }
                New-Object -TypeName PSObject -Property @{
                    Computer           = $WMI_OS.CSName
                    CBServicing        = $CBSRebootPend
                    WindowsUpdate      = $WUAURebootReq
                    CCMClientSDK       = $SCCM
                    PendComputerRename = $CompPendRen
                    PendFileRename     = $PendFileRename
                    PendFileRenVal     = $RegValuePFRO
                    RebootPending      = ($CompPendRen -or $CBSRebootPend -or $WUAURebootReq -or $SCCM -or $PendFileRename)
                } | Select-Object @SelectSplat

            }
            Catch {
                Write-Warning "$Computer`: $_"
                ## If $ErrorLog, log the file to a user specified location/path
                If ($ErrorLog) {
                    Out-File -InputObject "$Computer`,$_" -FilePath $ErrorLog -Append
                }
            }
        } ## End Foreach ($Computer in $ComputerName)
    } ## End Process

    End { } ## End End

} ## End Function Get-PendingReboot